Just use a standard Y harness, or a second channels on the receiver if you have an open channel and the ability to mix the throttle channel to the spare channel.
Using a reversing Y harness would result in one motor running full throttle with the throttle closed. A serious case of asymmetrical thrust
Pete

Probably sounded like a stupid question, but let me explain what happened! I had just received a second 100A ESC; however, it was a newer version of the same 'Sentilon' ESC. I had a programming card for the older version. Hooked the units up with a simple 'Y' and proceeded to run the motors up, each on 5S. Everything seemed to be o.k.! Then, I tried again and the newer motor started running in reverse, the older wouldn't run. Disconnected everything and tried to run the older ESC separate, Nada, nothing......... hooked up the programming card, no lights, nothing! Finally, after scratching my head and trying every combination, I checked the voltage on the Rx battery: 4.6V. Hhmmmm. Put it on the charger. It all works again. Apparently, that 4.6V can cause all sorts of wierd stuff. I just ran one motor on 10s and it spun the plane around in circles!